Testing of hair samples for the presence of indicators of drug use has gained importance not only for evidence gathering for criminal justice system proceedings but in pre-employment and post-employment screening of individuals. Unlike urine or blood sample testing which can provide only short term information concerning drug use by the tested individual and can therefore produce a negative result through abstention preceding the taking of the sample, hair testing can provide a long-term history of drug use for periods of, for example, ninety days or more preceding the taking of the sample. For this reason hair testing for drug use has become a reliable and important pre-employment or periodic test which cannot be defeated by short term abstention.
Heretofore testing of hair samples for drug use of marijuana by looking for cannabinoids such as tetrahydrocannabinol (THC) has been through techniques such as gas chromatography-mass spectrometry (GC/MS) and tandem gas chromatography-mass spectrometry (GC/MS/MS). These techniques not only qualitatively produce data indicative of the presence or absence of indicators of drug use from a hair sample but also quantify those results. These tests are expensive and time consuming. What is needed is a relatively fast and economical screening test which identifies clearly negative samples, i.e. samples with less than pre-determined threshold amounts of cannabinoids, from samples which are positive or not clearly negative. By performing a screening test of the samples, the necessity of performing complicated, expensive and time consuming assays including GC/MS or GC/MS/MS on determined negative samples would be obviated. Such assays would be reserved for those samples which, by the screening test, were either presumptively positive or otherwise not clearly identifiable as negative. Reserving the use of these assays to samples which are not identified by the screening test as clearly negative would result in savings in time and manpower for the laboratory providing the testing.
For radioimmunoassay, there is presented a problem of use and disposal of the radioactive isotope used in the assay.
An appropriate screening test, any such test is one which is forensically sustainable in its own right and accordingly must use generally accepted scientific techniques and principles.
Enzyme linked immunosorbant assay (ELISA) has been used for analyzing urine and blood samples to determine the presence of cannabinoids. ELISA is, compared to the other assay methods such as GC/MS and GC/MS/MS, relatively inexpensive, fast and accurate to quantitatively determine the presence of cannabinoid analytes indicative of use of marijuana. However, attempts to use ELISA as a screening test for cannabinoids in hair samples has heretofore been unsuccessful. ELISA relies upon immunospecific reactions of the analytes to test for the presence of substances. ELISA testing is well known, is described in U.S. Pat. No. 4,952,517 issued Aug. 28, 1990 and accordingly will not be described herein. It is believed that procedures heretofore used for obtaining and analyzing the hair extract containing cannabinoid analytes have been frustrated by adherence of these analytes or unknown amounts thereof on analytical surfaces resulting in the inability to correlate the results of the assay with the actual presence or absence of the analytes being tested for. Accordingly ELISA has not been successful as a test for cannabinoid analytes extracted from hair samples.